inet/inet_ntoa.c

   1 /* Convert Inet number to ASCII representation.
   2    Copyright (C) 1997 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Library General Public License as
   8    published by the Free Software Foundation; either version 2 of the
   9    License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Library General Public License for more details.
  15
  16    You should have received a copy of the GNU Library General Public
  17    License along with the GNU C Library; see the file COPYING.LIB.  If not,
  18    write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
  19    Boston, MA 02111-1307, USA.  */
  20
  21 #include <stdio.h>
  22 #include <stdlib.h>
  23 #include <arpa/inet.h>
  24 #include <libc-lock.h>
  25
  26 /* The interface of this function is completely stupid, it requires a
  27    static buffer.  We relax this a bit in that we allow at least one
  28    buffer for each thread.  */
  29 __libc_lock_define_initialized (static, lock);
  30
  31 /* This is the key for the thread specific memory.  */
  32 static __libc_key_t key;
  33
  34 /* Destructor for the thread-specific data.  */
  35 static void free_key_mem (void *mem);
  36
  37
  38 char *
  39 inet_ntoa (struct in_addr in)
  40 {
  41   static char static_buf[18];
  42   static int initialized = 0;
  43   char *buffer = NULL;
  44   unsigned char *bytes;
  45
  46   /* If we have not yet initialized the buffer do it now.  */
  47   if (!initialized)
  48     {
  49       /* Make sure there is only one process doing the initialization.  */
  50       __libc_lock_lock (lock);
  51
  52       if (!initialized)
  53         {
  54           if (__libc_key_create (&key, free_key_mem))
  55             /* Creating the key failed.  This either means we run
  56                have only a single-threaded application or something
  57                really went wrong.  In any case use a static buffer
  58                which is better than nothing.  */
  59             buffer = static_buf;
  60         }
  61
  62       __libc_lock_unlock (lock);
  63     }
  64
  65   if (buffer == NULL)
  66     {
  67       /* We don't use the static buffer and so we have a key.  Use it
  68          to get the thread-specific buffer.  */
  69       buffer = __libc_getspecific (key);
  70       if (buffer == NULL)
  71         {
  72           /* No buffer allocated so far.  */
  73           buffer = malloc (18);
  74           if (buffer == NULL)
  75             /* No more memory available.  We use the static buffer.  */
  76             buffer = static_buf;
  77           else
  78             __libc_setspecific (key, buffer);
  79         }
  80     }
  81
  82   bytes = (unsigned char *) &in;
  83   snprintf (buffer, 18, "%d.%d.%d.%d", bytes[0], bytes[1], bytes[2], bytes[3]);
  84
  85   return buffer;
  86 }
  87
  88
  89 static void
  90 free_key_mem (void *mem)
  91 {
  92   free (mem);
  93
  94   /* And we must set the data to NULL so that the destructor is not
  95      called again.  */
  96   __libc_setspecific (key, NULL);
  97 }